<!DOCTYPE HTML>
<html>
<script>
function verif(){
	var s=document.rad.checked ;
	if (!s){alert ("not checked");}
}
</script>
<head>
<meta charset="utf-8">
<title>radio2</title>
</head>
<body>
<input name="rad" type="radio" value="val1"/> value1 <br>
<input name="rad" type="radio" value="val2"/> value2 <br>
<input type="submit" onclick= verif();>
</body>
</html>